Normally, a lubricating oil is used to smoothly rotate a rotating shaft born by slide bearings or reciprocate a columnar-shaped shaft such as sliding valve discs used in slide valves, and consideration is taken so as to provide the lubricating oil with a function of preventing seizure with a cooling effect, by which heat generated is removed, in addition to functions of reducing frictional resistance, maintaining airtightness and so on.
When the lubricating oil becomes short, such cooling capacity decreases to cause a condition of partial seizure on an associated shaft. Because such partial seizure further impedes smooth flow of the lubricating oil, the entire shaft undergoes seizure and eventually rotation or reciprocation of the shaft is made impossible.
In order to prevent such accident, an oil groove or grooves are sometimes formed on the shaft surface to avoid a shortage of an amount of a lubricating oil. However, such measures are problematic in that as an operation goes on, a foreign matter such as abrasion debris or the like generated due to friction will accumulate in such oil groove or grooves to clog a flow passage of the lubricating oil, resulting in the lubricating and cooling function being impeded.